The forces required to hold molds closed may be considerable. This is particularly so in an injection mold where the force in the injection mold cavity produced by the molten plastic may exert a pressure of several thousand pounds per square inch. This force is transmitted to and has to be maintained by the frame supporting the mold clamps and molds.
The construction of molding machines, particularly including injection molding machines, thus required bulky frame members with a substantial member of welds. Such massive prior art constructions were costly to manufacture, and made access to the molds difficult so that there was excessive downtime.
In the Jomar Injection Blow Molding Machine, produced by Jomar Industries, Inc., Brigantine, N.J. 08203, a massive frame was required to support the injection mold clamp and the blow mold clamp. Certain clamp forces were generated outside the confines of the frame thus tending to cause undue stress and deflection or deformation in the frame. Further, access to the molds was difficult with excessive downtime in the maintenance and changing of the molds.
A more balanced control of the mold clamping forces was achieved by the three-station or delta construction, such as is shown and described in U.S. Pat. No. 3,877,859, granted Apr. 15, 1975 to Farrell and Grazine. This construction, however, was bulky and required three support posts and numerous weldments.
The art desired a simplified, compact (i.e. minimal floor space) construction, which is readily manufactured and assembled, and yet one capable of withstanding the clamp forces exerted during the injection molding operations. Further, the art desired an injection blow molding machine which provided ready access to the molds.